Pension and Other Post-Retirement Benefits - Expected Benefit Plan Payments (Details) $ in Millions	Dec. 31, 2020 USD ($)
Qualified Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
2018	$ 30.3
2019	29.6
2020	28.8
2021	29.9
2022	29.6
Years 2026-2030	134.6
Total	282.8
Nonqualified Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
2018	3.4
2019	3.7
2020	3.8
2021	3.8
2022	3.8
Years 2026-2030	17.5
Total	36.0
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
2018	2.3
2019	2.2
2020	2.0
2021	1.8
2022	1.7
Years 2026-2030	6.7
Total	$ 16.7